Two-Dimensional IV-V Monolayers with Highly Anisotropic Carrier Mobility and Electric Transport Properties

Two-dimensional (2D) semiconductors with anisotropic properties (e.g., mechanical, optical, and electric transport anisotropy) have long been sought in materials research, especially 2D semiconducting sheets with strong anisotropy in carrier mobility, e.g., n-type in one direction and p-type in another direction. Here, we report a comprehensive study of the carrier mobility and electric transport anisotropy of a class of 2D IV-V monolayers, XAs (X = Si or Ge), by using density functional theory methods coupled with deformation potential theory and non-equilibrium Green's function method. We find that the polarity of room-temperature carrier mobility μ of the 2D XAs monolayer is highly dependent on the lattice direction. In particular, for the SiAs monolayer, the μ values of the electron (e) and hole (h) are 1.25 × 10³ and 0.39 × 10³ cm² V^-1 s^-1, respectively, in the a direction and 0.31 × 10³ and 1.12 × 10³ cm² V^-1 s^-1, respectively, for the b direction. The computed electric transport properties also show that the SiAs monolayer exhibits strong anisotropy in the biased voltage in the range of -1 to 1 V. In particular, the current reflects the ON state in the a direction but the OFF state in the b direction. In addition, we find that the uniaxial strain can significantly improve the electric transport performance and even lead to the negative differential conductance at 10% strain. The unique transport properties of the 2D XAs monolayers can be exploited for potential applications in nanoelectronics.